In a construction machine such as a hydraulic excavator, generally, a front operating mechanism which is made up of a boom, an arm, a bucket, etc., and a swing body are operated by hydraulic actuators, e.g., hydraulic cylinders and hydraulic motors. Those hydraulic actuators are operated with supply of a hydraulic fluid from a hydraulic pump driven by an engine. The engine includes a fuel injector for injecting fuel into a combustion chamber (cylinder), and a governor mechanism for controlling the fuel injector. The fuel injection amount, the injection timing, etc. are controlled for control of engine output power.
When work environments (such as open air temperature, altitude, and solar radiation) of a construction machine are changed or when a work load is increased, or if any abnormality occurs in the engine, the exhaust temperature of the engine may rise correspondingly. If the exhaust temperature exceeds an allowable temperature in that situation, there occurs a possibility that engine parts (specifically, engine cylinders, an exhaust manifold, etc.) are damaged.
Hitherto, a method for avoiding such a possibility has been proposed which comprises the steps of detecting the exhaust temperature by a temperature sensor disposed in, e.g., an exhaust manifold, totalizing not only the number of times that the exhaust temperature has exceeded a first setting temperature at which the exhaust manifold may cause thermal fatigue, but also periods of time during which the exhaust temperature has exceeded a second setting temperature which is higher than the first setting temperature and at which the exhaust manifold may cause fracture due to oxidation, and issuing an alarm, reducing the fuel injection amount, or modifying the injection timing when the number of times of the excesses over the first setting temperature becomes over a predetermined value, or when the time representing the excess over the second setting temperature becomes over a predetermined time (see, e.g., Patent Document 1). In that prior art, a rise of the exhaust temperature is suppressed by reducing the fuel injection amount, or modifying the injection timing.    Patent Document 1: JP,A 8-319874